`toRawSql()` throws an exception on read-only connection

[xwillq]

Problem

Builder and Connection methods that return raw sql (toRawSql(), getRawQueryLog(), etc.) throw an error when connection is read-only. For example, with this configuration:

[
    'driver' => 'pgsql',
    'read' => [
        'host' => '...',
        'port' => '...',
    ],
    'write' => [/* empty */],
    // Other parameters, they don't have `host`, `port` or `url`.
]

I have this exception (code from tinker):

> DB::query()->from('users')->where('username', 'name')->toRawSql()

   PDOException  SQLSTATE[08006] [7] connection to server on socket "/var/run/postgresql/.s.PGSQL.5432" failed: No such file or directory
        Is the server running locally and accepting connections on that socket?

Reason

After some digging, I've found that enhanced connection uses getPdo() in order to escape strings:

laravel-postgresql-enhanced/src/Backports/ConnectionBackport.php

Line 93 in 816f36f

return $this->getPdo()->quote($value);

While Laravel's connection uses getReadPdo():
https://github.com/laravel/framework/blob/0b52acbdef545689017b6852c2b44918daeae9d3/src/Illuminate/Database/Connection.php#L1138

After changing that line in vendor, raw sql methods seem to be fixed, but I haven't done extended testing for other functionality, and I also don't know whether this is intentional or not, so I'm not sure if this change is enough to submit a PR.

[tpetry]

I've written the escape functionality in Laravel long after this one, so its definetely the more correct one. You can submit a PR.